An artificial lighting type of plant factory, which grows plants under an environment controlled in a closed system where a space is enclosed, has been developed. In such an artificial lighting type of plant factory, hydroponics, in which plants are grown with their roots (underground portions) immersed in water without using any soil, is mainly adopted.
In the above hydroponics, electric power is mostly used as a power source for main functions such as water-circulating and lighting. Accordingly, in the hydroponics, there arises a problem that even a short time period of power failure significantly affects a plant.
As a technique related to the hydroponics described above, patent literatures 1 and 2 described below are known.
The patent literature 1 discloses a bed for hydroponics in which a place for reserving a cultivation solution is provided. The patent literature 2 discloses an oxygen aerating device configured to supply a cultivation solution with oxygen when water-circulation is stopped.
Techniques disclosed in the patent literatures 1 and 2 are merely to consider how to supply water to part of a plant which is always immersed in water. There is no consideration about a case where electric power supply is stopped in hydroponics in which water, for example, in the form of mist is supplied to a plant. Accordingly, if the mist supply is stopped, there is a possibility of affecting a growth of the plant.
The present invention has been made with the foregoing situation taken into consideration. An object of the present invention is to provide a hydroponic cultivation device capable of maintaining water supply to a plant even when electric power supply is stopped.